The present invention relates generally to an imaging process. More specifically, a method for controlling the gloss on a printed image in a solid ink jet printer is disclosed. More specifically, the method applies to a two-step transfer and fusing process whereby in a first step a hot melt ink is applied onto an intermediate transfer surface and then transferred to a receiving substrate for creating an initial matte print image. This is followed by a fuse process wherein by changing the temperature and/or the dwell time and/or the nip pressure of the fuse operation, the gloss on the print image is changed.
For printing in a solid-ink printer, the simplest method of producing an output image is to propel droplets of ink onto a piece of paper to directly print the image onto the paper, i.e., a process known as direct printing. However, direct printing has many disadvantages. First, the head to paper gap must be adjusted for different media in order to control drop position. Second, there is the well-known paper hand-off problem between the rollers that guide the paper, because of the large size of the head. Third, there is a concern that head reliability will decrease because the paper is near the head. Also, to maximize print speed, many direct print architectures deposit the image bi-directional, which introduces image artifacts and color shifts. These problems are addressed with an offset, or indirect printing process. In this process, the ink is first applied to a rotating drum or other intermediate support surface and then transfixed off onto the paper wherein the ink goes on hot and then is fused. Therefore, a single drum surface transfers the image, spreads the ink droplets, penetrates the ink into the media, and controls the topography of the ink to increase paper gloss and transparency haze.
The process requires a delicate balance of drum temperature, paper temperature, transfix load, drum and transfix roller materials and properties thereof in order to achieve image quality. These combined requirements reduce the drum material possibilities mainly due to wear of weaker materials, which result in gloss and haze degradation. For most applications, a certain amount of gloss on a print is desired, but for some applications it is desirable to obtain either a very fine matte finish or a gloss finish. Unfortunately, the printer typically has to be designed around a single gloss finish that may be adequate for the typical users needs, but not for obtaining different gloss finishes. There are also undesired print and image quality trade-offs, which must be made when optimizing a printer for customer usage. For instance, between good gloss versus good image transfer.
To solve some of the above stated problems, ink jet printing systems have utilized intermediate transfer ink jet recording methods, such as that disclosed in U.S. Pat. No. 5,389,958 entitled IMAGING PROCESS and assigned to the assignee of the present application (the""958 patent) is an example of an indirect or offset printing architecture that utilizes phase change ink. The intermediate transfer surface is applied by a wicking pad that is housed within an applicator apparatus. Prior to imaging, the applicator is raised into contact with the rotating drum to apply or replenish the liquid intermediate transfer surface.
Once the liquid intermediate transfer surface has been applied, the applicator is retracted and the print head ejects drops of ink to form the ink image on the liquid intermediate transfer surface. The ink is applied in molten form, having been melted from its solid state form. The ink image solidifies on the liquid intermediate transfer surface by cooling to a malleable solid intermediate state as the drum continues to rotate. When the imaging has been completed, a transfer roller is moved into contact with the drum to form a pressurized transfer nip between the roller and the curved surface of the intermediate transfer surface/drum. A final receiving substrate, such as a sheet of media, is then fed into the transfer nip and the ink image is transferred to the final receiving substrate.
To provide acceptable image transfer and final image quality, an appropriate combination of pressure and temperature must be applied to the ink image on the final receiving substrate. U.S. Pat. No. 6,196,675 entitled APPARATUS AND METHOD FOR IMAGE FUSING and assigned to the assignee of the present application (the""675 patent) discloses a roller for fixing an ink image on a final receiving substrate. The preferred embodiment of the roller is described in the context of an offset ink jet printing apparatus similar to the one described in the""958 patent. In this embodiment, an apparatus and related method for improved image fusing in an ink jet printing system are provided. An ink image is transferred to a final receiving substrate by passing the substrate through a transfer nip. The substrate and ink image are then passed through a fusing nip that fuses the ink image into the final receiving substrate. Utilizing separate image transfer and image fusing operations allows for faster print speeds and improved print and image quality. For example, improved image fusing and improved image transfer efficiency and/or the ability to use reduced pressures, whereby the load on the drum and transfer roller is reduced.
This imaging architecture can be manipulated to serve a number of different markets. This is done through drum and motor sizing, increasing the number of printheads, and increasing the number of printhead nozzles, etc. Lower cost and lower speed printers could be designed for the consumer market, faster network business printers are possible, and very high speed production printers are also possible. However, the 2-step architecture with a separate transfer and fusing steps is particularly advantageous in the upper print speed arena due to its relatively simple operation with very high throughput. 100 ppm to 200 ppm printers are entirely possible. In this environment the customer becomes sensitive to a number of print and image quality attributes that might not be as important or specific in the consumer or business market. For example, low graininess, color quality, color consistency, and image durability are all important. Of equal importance in this arena is the level of image gloss. A high-end solid-ink product such as this must compete with other technologies such as the age-old offset lithography process (which has high gloss) and electrophotography (which typically has medium to low levels of gloss). Aside from trying to achieve the gloss that can be produced by any particular marking technology, there is the desire from the customer from different levels of gloss. There is simply an endless array of customers and customer applications. For example, advertisements, mailers, product documentation, books, and magazines. All of these different customers and customer applications can have different requirements for gloss. Therefore, what is needed is a process that could change the level of gloss without requiring a new mechanism or drastically different print process due to the high costs and complexity involved. By using an intermediate transfer surface and separating the transfer and fusing operations and by changing the temperature and/or the dwell time and/or the nip pressure of the fuse operation, the gloss on the print image can be changed. The present invention addresses this issue.
It is an object of the present invention to provide an improved imaging system which allows high quality gloss on a variety of media wherein the image is transferred and fused in serial which allows the fastest possible print speed.
It is another object of the present invention to provide an improved imaging system utilizing an intermediate transfer surface for producing a matte finish and a downstream fuser that is capable of operating at different temperatures and/or dwell times and/or nip pressures in order to produce a desired gloss finish.
It is yet another objective of the present invention to provide an indirect printing system for applying a compliant surface that increases the reliability of the printer, decreases the noise, decreases the cost of the release agent system and achieves improved print and image quality.
Accordingly, an application system is described for applying a two-step transfer and fusing process in an ink jet based imaging system whereby an ink image is applied onto an intermediate transfer surface and then transferred to a receiving substrate, followed by an independent secondary fuser. The secondary fuser operates at one or more temperatures and/or one or more pressures and/or one or more fusing speeds for processing the receiving medium having means for holding the final receiving substrate thereby allowing extending dwell times for increased cooling capabilities for facilitating hot fusing temperatures beyond the cohesive failure temperature of the ink.